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Title: Landscape position moderates how ant nests affect hydrology and soil chemistry across a Chihuahuan Desert watershed

item JAMES, A
item KOEN, T

Submitted to: Landscape Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2008
Publication Date: 11/15/2008
Citation: James, A.I., Eldridge, D.J., Koen, T.B., Whitford, W.G. 2008. Landscape position moderates how ant nests affect hydrology and soil chemistry across a Chihuahuan Desert watershed. Landscape Ecology. 23:961-975.

Interpretive Summary: Our study was conducted in September 2005 within a small watershed in the Jornada Basin, southern New Mexico, USA. The watershed is on the Chihuahuan Desert Rangeland Research Centre (CDRRC) of New Mexico State University, approximately 40 km NW of Las Cruces, Dona Ana County, N.M. The watershed is approximately 5 km in length, extending from the base of Mt Summerford downslope to an active alluvial basin adjacent to an ancient riverbed, which grades gently upslope to a sandy rise. We conducted our study at five sites within the watershed, along a SW-NE-trending transect about 6 km long from Mt Summerford in the south-west to a sandy rise in the north-east near South Well. These trends have implications for how we view the effects of ants on soil processes in arid environments. First, water infiltration was generally faster through nest soils than non-nest soils. Second, there were generally greater nutrient concentrations on nests compared with non-nests despite the fact that soil chemical properties varied markedly among the different sites.

Technical Abstract: Ants moderate the supply of critical resources such as water and nutrients in desert environments by changing the physical arrangement of soils during nest construction. We measured water infiltration and soil physical and chemical properties on and off the nests of two ant species (Pogonomyrmex rugosus, Aphaenogaster cockerelli) across five sites at differing landscape positions within a Chihuahuan Desert watershed. Our aim was to test whether the effects of these long-lived ant nests on water infiltration and soil chemistry varied between ant species or across sites within a watershed. Water flow was generally slowest at the site with the highest silt and clay contents, and fastest at the site with sandy soils. Flow was generally greater through ant nest soils than adjacent non-nest soils, and we attribute this to increases in macropores in the nests. However, the effects of both ant nests and species varied among sites. Despite wide variation in soil chemical properties across all sites, ant nests had a consistent effect on soil chemical properties, with higher levels of carbon, nitrogen, sulphur, phosphorus and electrical conductivity on nests compared with non-nest soils. Our results demonstrate that while we can generalise about the effects of ant nests on water flow and nutrient levels, differences in soil type, nest density and ant species across sites are likely to moderate these effects.